1. Technical Field
The present invention in embodiments generally relates to the art of image processing. The in embodiments shall be described in reference to electrophotographic applications, such as, for example, xerographic imaging. However, the invention can be applied in other areas, such as, for example, video image processing and lithographic systems.
2. References
In electronic imaging systems, images, such as, for example, pages of a document, are described in terms of high-level image or page description languages (PDL). Postscript™ is one such page description language well known in the art. In order to render an image, an image processor generates a binary image from the page description language description of the image. The binary image or bit map is in the form of a grid work or raster of mark/no mark decisions. The generation of a binary image from a page description language version of the image is referred to as raster image processing (RIP). In electrophotographic systems, a raster output scanner (ROS) controls a marking engine to place spots of ink, toner, or other colorants on a print medium according to the binary mark/no mark decisions indicated in the bit map.
To achieve high print quality, it is necessary to RIP documents to a high resolution. Typically, these resolutions are symmetric. For example, resolutions such as 600×600, 1200×1200, 1800×1800, or 2400×2400 dpi are common. For instance, these symmetric resolutions are supported by standard Postscript™ interpreters. However, due to optical and mechanical constraints and economic factors, raster output scanner (ROS) electronics are often designed to support asymmetric high addressable resolutions, such as 1200×600, 1800×600, 2400×600, and 4800×600 instead of the symmetric resolutions mentioned above. Occasionally, the reverse situation applies. In either case, a resolution conversion is required to make the output of the raster image processor (RIPer) compatible with the raster output scanner (ROS) electronics.
Any digital printer, digital front end (DFE), and fax machine can avoid objectionable artifacts associated with binary video path operations by encoding their halftone dots and decoding their binary. The encoding is used to avoid the generation of undesirable (highly stressful) binary patterns. In the past, these stressful patterns were created unintentionally, and print quality suffered.
Most digital front ends employ a standard rendering method, such as Postscript™. These methods typically produce symmetric resolution binaries such as 1200×1200. However, because of limitations associated with optics and characteristics of xerography, it is more appropriate to drive the ROS electronics of a printer with asymmetric high addressable binaries such as 2400×600. However, the required binary resolution conversion step (combined with optional binary rotation) can result in the creation of undesirable (highly stressful) binary patterns that significantly degrade pictorials. This can be avoided by using a symmetric halftone dot that is actually an encoding of an asymmetric dot, and by using the binary resolution converter as a binary decoder.